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Resistive force question using T (tension)

  1. Mar 25, 2013 #1
    1. The problem statement, all variables and given/known data

    A horse is pulling a canal boat using a rope at 12° to the direction of motion of the boat.
    The tension in the rope is 1150 N.
    (a) The canal boat is moving at a steady speed. Calculate the resistive force opposing
    the boat’s forward motion.

    2. Relevant equations

    Answer sheet gives equation as:
    T = T cos θ

    3. The attempt at a solution

    Solution is given as:

    = 1150 N x cos 12°
    = 1125 N
    Therefore resistive forces = 1125 N

    However I've tried two different scientific calculators. The windows version comes out at 13800 and googles version comes out at 970.43

    Am I using these tools incorrectly or are they flawed with calculations of this type?

    Many thanks, its driving me crazy!
  2. jcsd
  3. Mar 25, 2013 #2
    Hi Siliconwombat

    Your 970 answer : you've put in 12 rad instead of 12°
    Your 13800 answer : you've put in 12 instead of cos(12°) !!

    All it takes is a bit more care :-)
  4. Mar 25, 2013 #3
    Well i feel a little stupid on the first one!
    However on the second which was using the windows calculator I cant see any way of identifying the 12 as degrees? any hints?

    Think I'll have to buy a proper calculator again!

    You'll have to bear with me I'm coming back to physics after a long break to try and improve myself!

    Thanks for your help :)
  5. Mar 25, 2013 #4
    On my version of the Windows calculator, you can switch between "Standard" and "Scientific".
    For the latter, there are radio buttons to choose from Degrees and Radians.
  6. Mar 25, 2013 #5
    Actually scratch that, it seems to dislike my use of cos fullstop. Think Ill stick to google fr now ;)
  7. Mar 25, 2013 #6
    Yeah I'm set on scientific and degrees but no matter which way I input the equation it only gives me 1150x12. It seems to ignore cos completely.
  8. Mar 25, 2013 #7
    nvm its the opposite way round so input as 12 cos *1150.

    Thanks for your help and please disregard my stupidity :)
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